i will agree with the above adding deceleration to the mix. So, if the noise or pitch changes under any of the 3 conditions it is likely the gear set was not set up correctly. A noise on Decel is indicative of the pinion being to deep. the opposite is true under accel. I am not saying a hard accel or decel but rather a very slight increase either way while cruising on a flat road. Almost like adding or removing a feather from the gas pedal.
I will also comment that the noise would likely not be noticeable with the wheels off the ground as there is no load on the bearings or gears. While the noise is present a Sharp L or R turn will usually identify a bad bearing as you load or unload the bearings while doing so.
keep us posted